What happenedSen. Barack Obama delivered an impassioned speech at the Iowa Democratic Party Jefferson Jackson dinner over the weekend, giving his campaign for the Democratic presidential nomination a jolt as fresh polls showed the lead of front-runner Sen. Hillary Clinton had narrowed.

What the commentators saidIf Obama comes from behind to win the crucial Iowa caucuses in January, said David Yepsen in the Des Moines Register, his Saturday speech will be remembered as “one of the turning points.” Obama “contrasted himself with the others—especially Clinton—without being snide or nasty.” He tweaked Clinton for voting to authorize the Iraq war, and suggested she tells voters only “what they think they want to hear.” The digs should tip “some undecided caucusgoers his way,” and “help him close the gap.”

Obama has definitely “found his voice,” said Ana Marie Cox in Time.com. And that spells trouble for Clinton. “The speech mixed inspiration and contempt, passion and outrage, autobiography and attack”—with an echo of the “rich, poetic phrases” of Martin Luther King thrown in for good measure. The Democratic race has changed, because as Obama gained energy Clinton “trudged” through “momentum-sapping” nuisances, including “her supposed failure to leave a tip, the presence of a planted question in a town hall.”

The speech was fine, said Ruth Marcus in The Washington Post(free registration), but it was no “separating-from-the-pack moment.” In fact, Obama may find it difficult to continue jabbing at Clinton while still insisting that he is the candidate who will make Washington politics “less polarizing.” And while he, John Edwards, and the other rivals attack Clinton, she’s promising to “turn up the heat on Republicans,” something likely to appeal to the Democratic faithful. “Easier to say, of course, from the comfortable perch of her party's national front-runner.”